Generation of electric waves



April 1932- G. M, THURSTON 1,854,432

' GENERATI0N OF ELECTRIC WAVES Filed-Aug. 1s 1927 z Sheets-Sheet 1 Ha a3Arron/var April 19, 1932. I G. M. THURSTON 1,854,432

GENERATION OF ELECTRIC WAVES Filed Aug. 18. 1927 ,2 Sheets-Sheet 2 f JWMArron/var Patented Apr. 19, 1932 ITED STATES PATENT OFFICE GEORGE E.THURSTON, OF NEW YORK, Y., ASSIGNOR TO WESTERN ELECTRIC COM- PANY,INCORPORATED, OF NEW YORK, N. Y., A'CORPOBATION OF NEW YORK GENERATIONOF ELECTRIC WAVES Application filed August 18, 1927. Serial No. 213.778.

This invention relates to generation of electric waves.

cillator, operating at a given frequency, produces a harmonic wave ofthe given frequency and impresses the harmonic wave on a secondoscillator tuned approximately to the harmonic frequency. The harmonicpower from the first oscillator pulls the second oscillator into step,even though the pulling power may be very much smaller than the.

power in the second oscillator. Thus, a crystal controlled oscillator ofrelatively low frequency and power can stabilize the frequency of anoscillator of relatively high frequency and power.

If desired, the second oscillator can produce a harmonic of its basefrequency, and impress the harmonic on a third oscillator adjusted tooscillate approximately at the frequency of the latter harmonic. Thepower from the second oscillator can pull the third into step, eventhough pf lessmagnitude than the power in the third oscillator.Similarly, four or more oscillators may be employed, each after thefirst being controlled by a harmonic from the preceding oscillator.

Systemsof this type have important advantages over a system comprisingan oscillator feeding non-oscillatory harmonic pro-.

ducers or transmitters. For example, they require less power, and alsothey utilize singing and hence avoid any necessity for preventingsinging in high frequency amplifier circuits even though the frequencyof the second or subsequent oscillators may be higher than the maximumfrequency at which crystals can be operated satisfactorily.

Instead of having the controlling harmonics produced in the oscillatorsthemselves, non-oscillatory harmonic producers (that is, harmonicgenerators which do not produce self-sustained oscillations) may beinserted between the oscillators, to control the second oscillator fromthe first, etc.

Other objects and aspects of the invention will be apparent from thefollowing description and claims.

In the drawings, Fig. 1 is a circuit diagram of a system embodying oneform of the invention; Fig. 1A indicates a modification which may bemade in the system of Fi 1; Fig. 2 is a circuit dia ram of another ormof the invention; and gram of still another form of the invention.

In Fig. 1 an oscillator O1 comprises an iig. 3 is a similar dia-'electric space discharge tube 1. The fundamental frequency of theoscillator is determined largely by the capacity C and the inductance Lconnected in parallel in theplate circuit of the tube. The inductaiftecoil L is coupled to a feedback coil 10 in the grid circuit of the tube.

A harmonic of the oscillator frequenc is selected by'the capacity C andthe in notance L in parallel in the plate circuit, and is impressed onthe grid circuit of an .electric space discharge tube oscillator O2.

The oscillator O2 comprises an electric discharge tube 2 having acapacity C8 and an inductance L in parallel in its plate circuit. Theinductance coil L is coupled to the feedback coil 15 in the grid circuitof the tube 2. Oscillator O-2 tends to oscillate at a frequency set by Land C 'at approximately the desired harmonic of the first oscillator andas near to the harmonic selected by L and C as convenience in thesetting permits. The harmonic power from the first oscillator pulls thesecond one into step.

A harmonic of the frequency of the second oscillator is selected by thecapacity C, and the inductance L in parallel in the plate circuit, andis impressed on the grid circuit of an electric space discharge tubepower oscillator O3.

The oscillator O3 is shown as comprising two space discharge tubes 3 inparallel, coupled to an antenna 20 through an inductance coil 21 in theantenna and an inductance coil 22 in parallel with a capacity 23 in theplate circuit of the tubes. The coil 21 is coupled to a feedback coil 24in the grid circuit of the tubes. The frequency of the power osc llatoris determined largely by the antenna circuit and is very close to theresonant fre uency of L and C The harmonic power 0 the second oscillatorpulls the third one into step with the harmonic frequency.

Plate current is supplied to the oscillators from source 25, that fortube 1 asslng through inductances L and L,,, that or tube assing throughL and L and that for 3 passing through coil 22.

The grid circuit of each oscillator includes a condenser C, and a gridleak resistance R for supplying grid biasing potential. A condenser ineach oscillator by-passes high frequency current around the platecurrent source and prevents that source from polarizin the oscillatorgrid or grids.

The frequency of the primary oscillator O-'1 may be stabilized in anysatisfactory manner.

Undesired variations of the frequency of oscillator O-3 are preventedsince the controlling harmonic frequencies from oscillators 0-1 and 0-2synchronize oscillators O2 and O3 with those frequencies respectively.

Fig. 1A shows a modification of the connections shown in Fig. 1 betweenoscillators O1.and-O2. In Fig. 1A the capacity C, is across thesecondary, instead of the primary, winding of the coupling transformerincluding inductance L In Fig. 2, a Colpitts oscillator O1' has itsoscillation circuit, comprising inductance L in parallel with two seriesconnected capacities 0' tuned approximately to the mechanical resonancefrequency of a. piezo-electric crystal 40 which stabilizes theoscillator frequency. The source 25 supplies space current for tube 1through a choke coil 41 that has high impedance for the frequencies generated by O-1. A condenser 42 prevents this source from polarizing thecrystal.

A' harmonic of the oscillator frequency is selected by the capacity Cand the inductance L in parallel in the plate circuit, and is impressedon the grid circuit of a Hartley os- Icillator O2'.

Oscillator O2 tends to oscillate at a frequency set by its oscillationcircuit L and G at approximately the resonance frequency of L and G Theharmonic power of the first oscillator pulls the second one into step.

A harmonic of the frequency of the second oscillator is selected by thecapacity C, and the two inductances L';, and is impressed on the gridcircuits of each of tubes 3 of a pushpull electric space dischargeoscillator 0-3. The circuit constituted by capacity C in parallel withthe two inductances L in series, is connected in series in the platecircuit of oscillator O-2. One of the coils L impresses the harmonicvoltage fromoscillator 0-2 on the grid of one of tubes 3, and the otherof the coils L 4 impresses the harmonic voltage on the grid of the othertube 3 in opposite phase or si The oscillator 5 3' tends to oscillate ata frequency set by its oscillation circuit L and G at approximately theresonance frequency of C, with inductances L The harmonic power of thesecond oscillator pulls the third one into step. The source 25 suppliesspace current to the tube 2 through one half of coil L and coils L;

The connection 45 to the inductance L is intended to represent anysuitable load circuit for the oscillator O3', as for instance anantenna, or amplifier stages or a transmission line connected to anantenna.

' The inductance L is a bifilar coil comprising two strands 47 and 48.Condensers 49 connect the strands together at each end of the coil, andcondenser 30 connects the strands together at the middle of the coil.Each of these three condensers has low impedance for frequencies of theorder of the osc llation frequency; and the two strands 47 and 48 act asa single inductance at such fre uencies.

T e filaments of the two tubes 3 are conductively connected to themiddle of strand 48. The grid of one of the two tubes is conductivelyconnected to the filaments through a grid leak resistance and a portionof strand 48 at one side of the middle of the strand. The grid of theother tube 3 is conductively connected to the filaments through a gridleak resistance and a portion of strand 48 at the other side of themiddle of the strand.

Source 25 supplies space current for the tubes 3, the current for onetube passing through one half of strand 47 and the current for the othertube passing through the other half of strand 47.

Undesired variations in the frequency of oscillator 0-3 are preventedsince the controlling harmonic frequencies from oscillators O1 and 0-2synchronize oscillators 0-2 and O-3' with those frequenciesrespectively.

The circuits described above may well serve as high power short wavegenerators and yet be free from high frequency amplifiers. The harmonicsare produced in the oscillators themselves and taken out throughappropriate circuits and impressed upon the succeeding oscillators. Theprimary oscillator may be stabilized in any satisfactory manner orcrystal controlled as indicated in Fig. 2. In the systems of Figs. 1, 1Aand 2, the primary osc llator does not have to be any of thearrangements shown, even though crystal controlled, but may be of anyform in which there is an inductance in the circuit from which to getharmonics or in which an inductance or tuned circuit may be inserted toselect the harmonics.

In Fig. 3 a tuning fork oscillator O-51, operating ata frequency of, forexample,

1000 cycles a second, feeds an ampl'fier A62 which in turn feeds aharmonic generator HG-63. Oscillator 0-51 comprises a tuning fork 51actuated by a magnet 52 which has its winding included in circuit with acoil 53, a suitable source of current 54 and an interrupting orresistance changing 'devce 55 mechanically actuated by a tine of thefork.

The fork is thus arranged to automatically control the energization ofthe magnet 52 so that the action of the fork will be continuous tosupply a periodically variable current to the coil 53. Thecoil 53 iscoupled to a a coil 56 in the nput, circuit of amplifier A62. Theamplifier A-62 may be, for example, aspacedischarge amplifier operatingon the straight portion of its input voltageoutput currentcharacteristic. The harmonic producer HG-63 may be of any suitable type,as for example, the non-oscillatory electric space discharge harmonicgenerator disclosed in Vennes Patent. 1.485.650, March 4, 1924. In theoutput circut of the harmonic producer is a circuit 65 tuned to afrequency, say. 10,000 cycles per second. which is a harmonic of thefrequency of oscillator O-51.

A Hartley oscillator O70 comprising an electric space discharge tube 70has in its oscillation circuit a condenser 71 in parallel withinductance coils 72 and 73 in series.

The tuned circuit 65 is coupled to coil 73.

' and the oscillation circuit of tube 70 is tuned 35 approximately tothe same frequency as circuit 65. Therefore. the osc llator is heldv instep with the 10,000 cvcle current in circuit 65. although theoscillator output is much greater than the power of the controllingharmonic.

Space current for tube 70 is supplied. by source through a choke coil75, that has high impedance for the frequencies generated by 0-70.Condenser 7 6 is a stopping condenser which prevents battery 25 frombeing short circuited through coil 72. Condenser 77 in combination withresistance 79 produces proper biasing potent al for the grid of tube 70.A leak resistance 79 connects the grid and the filament of tube 70.

A harmonic generator I-IG85 comprising an electric space discharge tube85 has its grid and filament connected across resistance 7 9 by a seriescondenser 86 and a shunt resistance 87. A source 88 supplies a largenegative potential to the grid of tube 85 to cause the tube to generatepronounced harmonies. Space current for tube 85 is supplied by source 25through the output coil 90 of the tube. A condenser 30 by-passesalternating current around the source 25'. The harmonic producer doesnot generate selfsustainedoscillations.

A Hartley oscillator O9l comprising an electric space discharge tube 91has in its os cillation circuit a condenser 92 in parallel withinductance coils 93 and94 in series.

The coil 90 is coupled to coil 94, and the oscillationcircuit of tube 91is tuned approximately to a harmonic of the frequency of oscillator 0-70which is generated by harmonic'producer HG-85. Therefore, the oscillatoris held in step with that harmonic, although the oscillator output ismuch greater than the power of the controlling harmonic.

Space current for the tube 91 is supplied by source 25 through a chokecoil 39 that has high impedance for the frequencies generated by O91.The steady grid potential for this tube is determined by resistance 97.

A load circuit 95 of any suitable type is coupled to the coil 93 by acoil 96.

The power required to pull an oscillator into step depends upon the partof the circuit into which it is introduced and upon how much differencethere is between the pulling frequency and the frequency at which theoscillator tends to work. A system works well in which the current forpulling an oscillator into ste .is introduced into the oscillationcircuit 0 the controlled oscillator directly, as for example, at coils90 and 94in Fig. 3; .but the pulling power is more effective if thecontrol current is introduced in the grid circuits of the controlledoscillators, as for example, in Figs. 1 and 2. On some occasions it ispossible to pull an oscillator into step even when the frequency atwhich the oscillator tends to operate differs from the frequency of thecontrol current by as much as 10% and the pulling power is very muchsmaller than the power in the controlled oscillator. In arrangements asindicated in any of the figures of the drawings, the differentoscillators or stages do not have to be of the same power capacity but,as is indicated above, may actually increase in power from the firsttowards the last and still secure frequency control.

What is claimed is:

1. In combination, an electric space discharge device, means for causingsaid device to generate self-sustained oscillations of fixed frequency,and an oscillation generator cou- 1-15 pled to said device, included insaid last mentioned means, the power capacity of said device being largerelative to that of said oscillation generator.

2. In combination, an oscillator of relatively low power capacityoperating at a relatively low frequency, a second oscillator ofrelatively high power capacity, tuned ap proximately to a harmonic ofsaid first frequency, means included in said first oscillator itself forproducing said harmonic, and means coupling said oscillators forimpressing said harmonic from said first oscillator on said secondoscillator, whereby said first oscillator stabilizes the frequency ofsaid second oscillator without the interposition of non-oscillatory highfrequency amplifiers.

3. In combination, an electric s ace discharge device, means for causingsaid device to generate self-sustained oscillations of fixed f uency,and an oscillation generator coupie to said device, included in saidlast mentioned means, the power capacity of said device being largerelative to that of said oscillation generator, eluding mechanicallyvibratile means stabilizing its frequency.

4. A si aling system comprising a relatively hig power oscillator, anoscillator for delivering relatively low power at a frequency havingless variation than the frequency variation that said first oscillatorwould undergo in the absence of said second oscillator, and meanscoupling said oscillators for stabilizing the frequency of said firstoscillator, the frequency to which one of said oscillators is tunedhaving an integral multiple of a frequency at which the other is tuned.

5. In combination, a generator of a wave of a fundamental frequency, agenerator of a frequency equal to a harmonic of the fundamentalfrequency, means responsive to the single wave constituted by said waveof fundamental frequency for converting the fundamental frequency waveinto a wave of a frequency which is a harmonic of the fundamentalfrequency equal to the harmonic generated by said second generator, andmeans for so inter-relating said converting for and said generatorintively stable frequency,

connected to said generator to maintain substantially constantthefrequency thereof, a generator of waves of an approximately harmonicfrequency, and means coupling said generators whereby the harmonicfrequency is maintained constant.

9. In combination, an electric space discharge device means for causingsaid device to generate self-sustained oscillations of relaanoscillation generator of less stability and ofan approximately harmonicfrequency, means responsive to said first oscillations to produce aharmonic thereof of approximately the fre uency of said oscillationgenerator, means for impressing said harmonic oscillations on saidgenerator whereby the frequency stability of the latter is improved;

10. In a radio transmitting system, a plurality of amplifiers in tandem,each amplifier including a space discharge tube arranged to generateoscillations, resonant means individual to each tube for controlling thefrequency of oscillations in each tube, and means cooperating with allsaid resonant means for maintaining the frequency of oscillationssubstantially constant.

In witness whereof, I hereunto subscribe my name this 16th day of AugustA. D., 1927.

GEORGE M. THURSTON.

means and said second generator that the frequency of said secondgenerator is maintained in synchronism with the harmonic produced bysaid converting means.

6. A signaling system comprising a relatively high power oscillator, anoscillator for delivering relatively low power at a frequency havingless variation than the frequency variation thatsaid first oscillatorwould undergo in the absence of said second oscillator, and anon-oscillatory harmonic generator coupling said oscillators forstabilizing the frequency of said first oscillator, the frequency towhich one of said oscillators is tuned being an integral multiple of afrequency to which the other is tuned.

7. In combination, an oscillation generator operating at a relativelylow frequency, a second oscillation generator tuned approximately to asecond frequency which is a harmonic of said first frequency, anoscillator adjusted to oscillate approximately at a third frequencywhich is a harmonic of said second frequency, means for causing saidfirst oscillation generator to control'the frequency of saidsecond'oscillat-ion generator, and means for causing said secondoscillation generator to control the frequency of said oscillator.

8. In combination, a generator of continuous oscillations, mechanicallyvibratile means

